Tells me what I need to know. I will double it to have the security.
My multichannel a/d is in sync to a level within your spec. I will
setup with a 100' legs on a triangle and see how the rest goes.
I do want to stay within 44.1 sample rate because I am not hard drive
rich. I fill those critters up as fast as I buy them and can not
afford enough. I do not want to fill up more than 1 drive per day
with only one drive devoted to the task. MN police are not the
federal gov as we in MN still hold the law to the law. But, a call
from a civilian is still responded to without a need to determine
privacy issues regarding a policy methodology of information gathering.
Rich
--- In Steve Pelikan <>
wrote:
>
> Rich:
>
> I live in a city so I hear lots of hand guns too. But I'm always pretty
> sure where
> the shots are coming from: the 24 hour store on the corner.
>
> Here's back-of-the envelop stuff to see if we're close enough to what
> you could do to make more calculation
> worth it. The basic geometry is sketched in
> (http://math.uc.edu/~pelikan/Dora/Instructions.html)
>
> A formula for finding a bearing theta to a distant object based on time
> of arrival of sounds at two microphones is
>
> theta =3D arcsin( V dt/D) here V=3Dspeed of sound, D is distance betwee=
n
> mics and dt is difference in time of arrival.
>
> To locate something to within 100 feet at a mile means getting the
angle
> right to a couple degrees.
>
> This boils down to (assuming middling values of theta and V=3D333 m/sec)
>
> D =3D (333/0.02) X
>
> where X is how accurately the time of arrival difference can be
> measured. With values between 0.001 sec (generally easy to do) and
> 1/(22050) (very tricky to do with 44.1KHz sampling) this gives D in the
> range 1 -17 meters. How well you can "align" the tracks pretty much
> determines X --- gunshots should be pretty easy, but ambient noise
(like
> wind) makes things harder.
>
> With 3 microphones the baselines for the pairs are all oriented
> differently and usually one pair has an unfortunate value of theta. So
> probably you'd be looking at trying to put mics at the corners of an
> equilateral triangle with side length on the order of 30 feet or so.
>
> Don't start hauling cable! But if this is close to doable, let me know
> and I'll get out a calculator.
>
>
> Thanks,
>
> Steve P
>
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